Have the rear control arm replaced. The car will have a much better feel to it. Left unattended, it could even be dangerous if the wear accelerates.
The rear main seal simply keeps the oil from getting out of the engine. If it's leaking it'll make a mess under your car and anywhere you park. Keep the oil level up in the engine. Replace the rear main when you can't stand the mess anymore, or until something else gives up in the engine.
95 E320 Cabriolet, 131K